Hydrocracking process producing lubricating oil



bricating oils by chemical treatment.

United States Patent Otlice 3,308,055 Patented Mar. 7, 1967 3,308,055HYDROCRAtIKlNG PRUCESS PRODUCING LUBRICATING OIL Robert H. Kozlowski,Berkeley, Caliih, assignor to Chevron Research Company, a corporation ofDelaware Filed Apr. 13, 1964, Ser. No. 359,057 7 Claims. (Cl. 208111)This invention relates to catalytic hydroconversion processes forupgrading hydrocarbon oils. More particularly, the invention relates toprocesses for hydrocracking heavy petroleum oils and to processes forproducing lubricating oils.

A variety of schemes have been proposed from time to time for producinglubricating oils from less suitable oils by catalytic hydroconversion orhydrotreating processes. In general, such processes involve contacting aselected hydrocarbon oil feed, such as a petroleum fraction, withhydrogen in the presence of a catalyst, at conditions of elevatedtemperature and pressure found to improve the properties of the oil feedwith respect to its use as a lubricant. For example, mild hydrogen treating has been used to improve the stability of lubricating oils byhydrogenating hetero organic compounds, such as sulfur and nitrogencompounds responsible for the poor stability of the feed. More severedestructive hydrogenation, involving both hydrocracking andhydrogenation, has been proposed as a substitute for one or more of thesolvent extractiomacid treating, and clay contacting stepsconventionally employed in the production of lu- The destructivehydrogenation processes remove a portion of the aromatics and condensedring compounds by ring-scission with limited side chain removal byhydrocracking to lower boiling distillates.

It is characteristic of such processes that the feedstocks employed arecarefully selected, the selection being generally restricted to oilswhich are already recognized as lubricating oils or as good conventionalsources for lubricating oils. For example, to produce lubricating oilsof very high viscosity index, it has been necessary to employ as thefeed an oil which already has a moderately high viscosity index. Thus,high quality crude oils are segregated for use specifically in preparinglube oils, whether by hydrofining or by chemical treatment. Further,previously known and proposed processes are each designed to be operatedfor the production of a particular type of lubricating oil product.Accordingly, it has been necessary to size the treating process tohandle a quantity of oil corresponding closely to the expected productdemand. Since lubricating oils are a small volume product as compared toother petroleum refinery products such as gasoline, kerosene, heatingoils, and chemicals, the practical application of many of the proposedprocesses is seriously limited by economics. Catalytic hydroconversionprocesses operating at elevated temperature and pressure are quiteexpensive and diflicult to justify economically except for processinglarge quantities and unless a tremendous upgrading in the value of theproducts as compared to the value of the feed can be accomplished. Thus,the lube hydrotreating processes are generally restricted to mildhydrofining carried out at only moderate temperatures and pressures,with short contact time between the oil feed and catalyst to minimizethe size of the equipment. As a further consequence of the economicsituation, the processes heretofore proposed strive to obtain thehighest possible yield of product lubricating oil from the oil feed.Even in severe destructive hydrogenation processes where distillatefuels of some value are produced as a by-product, it is necessary tocontrol the operation of the process with respect to obtaining thedesired quality in the major lubricating oil product, and both thequality and amount of other products be permitted to fall where theymay. This is another reason why it has been necessary to select thefeedstock carefully, and to design a particular process installation fortreating the particular selected feed.

The present invention provides a process whereby good lubricating oilsand lubricating oil base stocks can be produced from nearly any heavyhydrocarbon oil feed as a by-product of hydrocracking. In particular,the invention provides a method of producing lubricating oil base stockfrom a heavy, high-boiling, oil which is normally unsuitable for any useexcept as an ingredient of heavy fuel oil; In one embodiment theinvention provides a hydrocracking process for upgrading heavy fuel oilcharacterized by always producing a superior lubricating oil by-product.The principal products in terms of volumetric yield are high valuedistillate fuels, and consequently the invention makes possible the useof a large plant wherein the economies are more favorable. A particularfeature ofthe invention is that it provides a process wherein there isconsiderable flexibility and latitude permitted in adjustingindependently both the yields and the qualities of the lubricating oiland distillate fuel products.

In accordance with the invention, it is found that by hydrocracking aheavy oil feed together with a heavy recycle oil, controlling conditionsso as to accomplish only a controlled per pass conversion to distillatefuels, limiting the withdrawal of products boiling in the boiling rangeof the heavy oil feed, and providing adequate heavy recycle oil, theviscosity index of products boiling in the lubricating oil range can bemade to increase far above that which would otherwise be obtained.Furthermore, the conversion, product withdrawal, and recycle ratio canbe independently adjusted within substantial limits to compensate forchanges in such factors as feed quality and demand for differentproducts, without serious eifect on product qualities. In a preferredembodiment of the invention, a heavy fuel oil is converted entirely tolower boiling distillates and improved lubricating oil base stock byhydrocarcking the heavy fuel oil and a heavy recycle oil in a volumeratio of heavy recycle to heavyfuel oil between 0.3 and 1.5. Thehydrocracking is carried out in a catalytic hydrocracking reaction zoneat conditions for converting between 25 and of the combined fuel oil andrecycle oil to distillates boiling below 700 F. The entire normallyliquid hydrocarbon oil effluent of the hydrocracking reaction zone isdistilled to separate said eflluent into lowerboiling distillates and aremainder. At least a portion of this remainder is then furtherdistilled, and there is recovered therefrom a lubricating oil base stockof which an amount corresponding to between 2% and 25% of the heavy fueloil feed boils within the boiling range of the feed. The aforesaid heavyrecycle oil is formed by combining each portion of the aforesaidremainder which was not so distilled with at least each highest-boilingportion of said remainder which was so distilled but not recovered aslubricating oil base stock.

It is found that by processing in accordance with the inventionlubricating oils of higher viscosity index can be produced than areproduced by known processes applied to similar feeds. More particularly,it is found that by the process of the invention there can be producedoils of acceptable viscosity .index for use in lubricating oil fromextremely low grade oils, including oils having very low, even negative,viscosity indices. Although the lubricating oil or lubricating oil basestock is obtained 7 in relatively low yield, it is obtained in a processdesigned for high throughput, and consequently there are adequateproduction quantities. Thus, the invention avoids the need to segregatespecial quality crude oils or portions thereof for lubricating oilproduction.

The attached drawing illustrates an arrangement of flow paths and majorprocess units as they appear schematically in a preferred embodiment ofthe invention. The following description of the drawing servesparticularly to clarify the manner in which the hydrocracking reactionzone efll-uent may be worked up.

A heavy oil feed in line 11 and a heavy recycle oil in line 12 are bothfed to a hydrocracking zone, for example, by combining them in line 13.Hydrogen is also continually supplied to the hydrocracking zone throughline 14. In a typical hydrocracking zone, as shown, the makeup hydrogrenis combined with a recycle hydrogenrich stream 15 to form ahydrogen-rich gas in line 16, which is then passed into reactor 18together with the feed and recycle via line 17. The oil and hydrogen aresupplied preheated and at elevated pressure by means of conventionalfurnaces, heat exchangers, pumps, and compressors not shown. In general,engineering details have been omitted entirely from the drawing becausethey are subject to being incorporated in innumerable arrangernents andpermutations, all within the skill of the art. Reactor 18 contains ahydrocracking catalyst in the form of small particles, whereby the oilis in intimate contact with the catalyst and hydrogen during passage ofthe oil therethrugh, the time of contacting and the temperature andpressure conditions being such that between 25 and 75 of the combinedfeed and recycle are converted to lower boiling distillates. As usedherein, the conversion is determined by comparing the volume ofdistillates produced which boil below 700 F. with the volume of materialin the combined feed and recycle which does not boil below 700 F.Conversion thus excludes overlap material which may appear in thedistillates withdrawn.

The entire eifiuent of reactor 18 passes via line 19, usually beingcooled while so passing, to separation zone 20, wherein hydrogen-richgas is separated for recycling through line 15. The normally-liquidhydrocarbon effluent then passes through line 21 to distillation zone22.

In distillation zone 22, which may include one or several columns, theeffiuent is distilled, generally at atmospheric or superatrnosphericpressure, to separate light gases and low-boiling hydrocarbons,designated by line 23; distillate fuel fractions such as gasoline,designated by line 24; and distillate fuel fractions such as kerosene orother middle distillates, designated by line 25. In general, alldistillate fuels boiling below about SOD-550 F. produced byhydrocracking are recovered in this first distillation, leaving aremainder in line 26. The distillates recovered, however, may alsoinclude all material in the hydrocracking zone efiluent boiling belowabout 650-700" F., corresponding approximately to the minimum initialboiling point of lubricating oil produced by the process of thisinvention. That is to say, the distillates boiling below about 700 F.obtained in the process usually have greater valve as distillate fuels,or as intermediate feeds to be further converted to higher value fuelsby subsequent processing, than as lubricating oil.

At least a portion of the so-called remainder in line 26 is passedthrough line 27 to vacuum distillation zone 28, which may comprise oneor more columns. Because of the lower pressure, and if the firstdistillation is carried out so as to leave materials boiling below about650-700 F. in the remainder, a distillate is obtained overhead in line29. It is desirable to remove this distillate to control the fiash pointand/or initial boiling point of the lubricating oil products. Thisdistillate or a portion thereof may be passed via line 30" to form aportion of recycle stream 12. Alternately, however, all or a portion ofthe distillate in line 29 may be withdrawn via line 31 and recovered asa salable gas oil or heavy middle distillate. The amount of any portionso recovered which boils below 700 F. is included as a part of thedistillate fuel products in controlling the hydrocracking so as toconvert between 25 and of the combined feed and recycle to saiddistillate products.

From distillation zone 28 there may be withdrawn cuts of one or moredistillate lubricating oils as indicated by line 32. The boiling rangeof the cut or cuts withdrawn as through line 32 is controlled withreference to the viscosity desired. For example, there may be withdrawntwo distillate lubricating oils or lubricating oil base stocks havingthe properties of, and suitable for use as or in, a neutral and a 480neutral, boiling respectively from about 700 to about 800 F. and fromabout 800* to about H 900 F. The term lubricating oil base stock is usedherein as indicating that in some cases it will be desirable to furthertreat the oil, as by solvent extraction and/or dewaxing, in order totake maximum advantage of the improved oil qualities and producesuperior lube oil.

From that portion of the remainder in line 26- which was passed throughline 27, and thus distilled in zone 28, there is obtained ahighest-boiling portion in line 33-. In the case where only a portion ofthe remainder in line 26 was so distilled, all or a portion of thishighest-boiling portion in line 33 may be recovered as a lubricating oilbase stock in line 34'. For example, when the feed in line 11 is adeasphalted residuum, a bright stock may be recovered in line 34. In thecase where all of the remainder in line 26 is passed through line 27 andso distilled, only a portion of this highest-boiling portion in line 33can be recovered through line 34. Any portion of this highest-boilingportion in line 33 which is not recovered as lubricating oil base stockin line 34,- i.e., all the rest, is to be combined with any portion ofthe re mainder which was not vacuum distilled, i.e., the entire portionin line 35, thereby forming line 37, for use in forming the recycle oilin line 12. In order to adjust the properties of lubricating oilrecovered in line 34, such as viscosity and initial boiling point, morematerial may be distilled in zone 28 and taken off by line 32 than it isdesired to recover as lubricating oil having the properties of thematerial in line 32. In that case, a portion of the material in stream32 is diverted through line 36, which is also used in forming therecycle oil. In many cases the diversion of material through line 36 tohelp form the recycle oil is necessary in order to avoid withdrawing anamount of total lubricating oil products, boiling in the range of freshfeed in line 11, corresponding to more than 40 volume percent of thefresh feed. Thus, in forming the recycle oil in line 3-7, there is usedany portion of the remainder 26 which is not distilled under vacuum,i.e., any portion in line 35, and also any remaining highest-boilingportion of the material which is so distilled, i.e., the portion of line33 not recovered as lubricating oil in line 34, and there will also beused any distillate boiling in the feed boiling range which is notrecovered as lubricating oil, i.e., the portion in line 36. Incombination with the material in line 37 there may also 'be used informing the recycle oil in line 12 the distillate in line 30, asmentioned previously.

As feed to the process of this invention there may be employed virtuallyany high boiling heavy hydrocarbon oil derived from petroleum or similarhydrocarbonaceous materials of ancient origin. By high-boiling is meantthat a substantial portion of the feed, at least 30%, does not boilbelow about 800 F. That is, if the feed is distilled, a substantialportion will not yet have boiled over when the temperature has reached800 F. (corrected to atmospheric pressure distillation). Preferred oilfeeds boil substantially entirely above about 650-700 F., disregardingthe initial low-boiling such as heavy vacuum gas oil distillates ofcrude petroleum having end points in the range 1000-1150" F. The initialboiling point of the preferred feeds may be 900 F., or higher, and thefeed may have no definite end boiling point. Thus, for example, the feedmay be a solvent decarbonized residuum, such as the oil obtained bypropane deasphalting a short residuum. In the case of residuals, theasphaltenes at least should first be removed as by solvent extraction orprecipitation to form a suitable feed for this process, to prevent toorapid coking of the hydrocracking catalyst. It will be noted, however,that included within the suitable feeds are materials which wouldnormally be unsuited for any use other than as ingredients of heavy fueloil. Freedom from asphaltenes is based on the desire to have a longon-stream time between catalyst regenerations, not because they preventproduction of improved lubricating oil. Consequently, how completelyasphaltenes are to be removed is a matter of degree, affecting theeconomics, but not the essential nature of the process. Use of the termoil in referring to the feed and other streams means that liquid phaseconditions exist at the process conditions, and it is not meant to implythat the feed cannot be solid or semisolid at room temperature.

The heavy recycle oil, having been prepared as previously described,will contain no substantial amount of materials boiling below the endboiling point of kerosene or jet fuel, i.e. 500-550 F., and usually willcontain no substantial amount of materials boiling below 650700 F. Therecycle will always contain at least some of the highest-boilingmaterials fed to or produced in the process. The initial boiling pointof the recycle may, however, be below, the same as, or above the initialboiling point of the feed, depending on whether any lubricating oilproduct is withdrawn which contains material boiling below the initialboiling point of the feed, and depending on whether salable gas oil(line 31 in the drawing) is recovered. It is also possible for therecycle oil to have a vacancy in its distillation curve, if all of theremainder from the first atmospheric or pressure distillation isdistilled under vacuum and there is recovered a lubricating oil productcomprising all materials boiling in a particular narrow boiling range,for example, from 800 to 900 F. It will be appreciated, however, thatthe many possible variations in recycle properties, and in recovery ofproducts, are restricted by the need to provide recycle oil in a ratioto fresh feed of between 0.3 and 1.5 volumes of recycle per volume offeed. Also, equivalent results are not obtained in all such permissiblevariations. Thus, it is preferred for optimum lube oil properties torecover lube oil in a yield of only 220% and to provide heavy recycle ina ratio to fresh feed between 0.5 and 1.25.

The heavy oil feed and heavy recycle oil are hydrocracked by passingthem and hydrogen through a catalytic hydrocracking reaction Zone atelevated temperature and pressure to contact therein a hydrocrackingcatalyst. Suitable hydrocracking catalysts for use in the process ofthis invention are those solid contact materials having the propertiesof accelerating scission of carbon-carbon bonds and of acceleratinghydrogenation of cracked hydrocarbon fragments so produced. Also, sincethe feeds to be processed are generally oils containing hetero organiccompounds of nitrogen, sulfur, oxygen, and even metals in some cases,the catalyst must be one whose cracking and hydrogenation activities arenot rapidly or permanently impaired by such compounds or theirdecomposition products. Thus, in particular, the catalyst must be onewhich is relatively insensitive to nitrogen contaminants. Also, forpurposes of the present invention in its preferred aspects, it is highlyadvantageous to employ a catalyst which maintains high activitythroughout continuous operation for long periods of time of at least 600hours, and more preferably in the neighborhood of from two to severalthousand hours, without regeneration. These requirements are met by manyknown catalysts, which usually are composed of a refractory oxide incombination with an active hydrogenating metal component of Group VIIIof the Periodic Table and a hydrogenating metal component of Group VI ofthe Periodic Table. It is generally desirable to convert the metalcomponents to the sulfides to develop their maximum catalytic activityfor hydrocra-cking oils containing nitrogen compounds.

Particularly good refractory oxides are the high surface area porousoxide cogels or copreci-pitates of silica with alumina or magnesia,wherein the silica and the alumina or magnesia are each present to theextent of at least 10%. Other high surface area cogels with materialssuch as zirconia, titania, or boria can also be used. The singleingredients alumina, silica, or magnesia do not themselves appear tohave sufficient cracking activity to be considered within the preferredrefractory oxides. Preferred Group VIII components are the oxides andsulfides of the iron group and noble metals, cobalt, nickel, platinum,and palladium, but specially nickel. Preferred Group VI components arethe oxides and sulfides of molybdenum and tungsten. Thus, examples ofhydrocracking catalysts which would be preferred for use in the processare the combinations nickel-tungsten-silicamagnesia,nickel-tungsten-silica-alumina, nickel-molybdenum-silica-alumina, andnickel-molybdenum-silica-magnesia. Such catalysts may vary greatly intheir activities for hydrogenation and for cracking and in their abilityto sustain high activity during long periods of use depending on theircompositions and methods of preparation. Obviously, the best provencatalyst available is selected, taking into consideration all of theabove factors and also price.

Numerous schemes can be devised for bringing together the oils,hydrogen, and the catalyst at the temperature and pressure conditionsfor catalytic hydrocracking. Thus, the catalyst may be suspended in theoil as finely divided particles, or it may gravitate through the oil asrelatively large particles. The oil and hydrogen may be passed upwardsor downwards concurrently or countercurrently in one or more parallel orseries-connected reaction chambers. Probably the most suitablecommercial method for carrying out the process continuously, however,comprises preheating the oil and hydrogen under pressure and thenpassing them downward through one or more stationary beds of catalystparticles contained in a high pressure reactor. The amount of hydrogenpassed through the reactor is in substantial excess of the amountconsumed in hydrogenation reactions occurring therein, and the gas usedis sufficiently pure, so that the hydrogen partial pressure at all timesconstitutes the major portion of the total pressure. In some caseshydrogen consumption may exceed 1700 standard cubic feet per barrel offresh feed, and accordingly there should be provided at least 2000standard cubic feet of hydrogen per barrel and most preferably 4000standard cubic feet or more.

Hydrocracking reaction conditions are preferably controlled in theranges 700850 B, 1000-4000 p.s.i.g., and flow rate of 0.33 volumes ofcombined feed and recycle per hour per volume of catalyst so as tothereby convert between 25% and 75% of the combined heavy oil feed andheavy recycle oil which does not boil below 700 F. to distillate fuelswhich boil below 700 F. Thus, for example, if 10% of the combined freshfeed and recycle boils below 700 F., that portion is ignored incalculating the conversion, which is arrived at by comparing the volumeof net products boiling below 700 F. with the volume of combined freshfeed and recycle which does not boil below 700 F., i.e., the 90%.Likewise, if the combined feed and recycle has an initial boiling pointabove 700 F., for example 800 F., materials formed in the boiling range700800 F. are not included in calculating the conversion even though aproduct stream may be withdrawn comprising materials boiling in therange 700800 F. Since materials would not be included in the measurementof distillate fuels boiling entirely below 700 F., nor would they beincluded in the measurement of lubricating oil product boiling above theinitial boiling point of the feed. This amount does not escapeaccounting in the process of the invention, however, because in additionto the requirement of between 25% and 70% of the combined feed andrecycle which does not boil below 700 being converted to distillatefuels boiling below 700 F, and the requirement that an amount oflubricating oil boiling within the feed boiling range corresponding tobetween 2 and 40 volume percent of the feed be withdrawn, there is thefurther requirement that an amount of heavy recycle oil be provided in aratio between 0.3 and 1.5 volumes per volume of fresh feed. It ischaracteristic of the hydrocracking reactions that in order for theconversion as defined herein to be at or near the lower limit of 25% theratio of recycle to feed will be near the upper limit of 1.5; forconversion near 75 the ratio will be near the lower limit of 0.3.Consequently, the amount of distillate boiling above 700 F. and belowthe initial boiling point of the feed which can be withdrawn willgenerally be limited to less than the difference between the amount ofhigher-boiling lubricating oil actually withdrawn and the 40% yieldwhich might have been withdrawn. That is, such a distillate productdisplaces lube oil product.

The higher the total conversion, the greater the proportion of lightproducts, i.e., boiling below 400 F. It is frequently desired, however,to produce a greater proportion of middle distillate products, i.e.,boiling between 400 F. and 700 F. Preferably the hydrocrackingconditions are such as to convert an amount between 20% and 40% of thatportion of the combined feed and recycle which does not boil below 700F. into hydrocarbon oil which boils between 400 F. and 700 F., and toconvert no more than an equal amount but at least about 10% of saidportion into normally liquid (C hydrocarbon oil which boils below 400 F.The above description of the preferred conversion ratios does not implythat there must actually be recovered one product boiling from justabove the boiling point of butane to 400 F. and another product boilingfrom 400 F. to 700 F., but that the amounts of such materials which areformed can be ascertained by sampling and distillation of the samples.Description of'the conversion in these terms defines a situation whereinthe amount of middle distillate produced equals or exceeds the amount ofgasoline produced, and thereby defines a preferred controlled type ofhydrocracking wherein primarily only the largest and most complexmolecules in the oils are acted upon, and over-cracking of theintermediate-boiling-range product is avoided. In this way, superiorlubricating oil and superior distillate fuels are produced in theprocess of the invention.

If conversion to 400-700 F. distillate is much less than 20%, as mayoccur either by the total conversion to distillates boiling below about700 F. being too low or by the conversion to gasoline by overcrackingbeing high, the improved results may not be obtained. If conversion istoo low, there will not be enough hydrocracking occurring to increasethe viscosity index appreciably above that obtainable without theprocess of the invention. Likewise, if the conversions are too high, asby use of a high temperature, product quality suffers particularly inthe 320-550 F. boiling range, where increased aromaticity renders theproduct less desirable for jet fuel.

In the fixed bed process the reactor efiiuent comprising the reactionproducts and excess hydrogen is cooled, and excess hydrogenrich gas isseparated for recycling. The distillate fuel products are then separatedfrom a higher boiling remainder by distillation. The distillate fuelfractions thus separated and recovered include all normally liquid oilin the hydrocarbon effluent boiling in and below the kerosene boilingrange. This first distillation may be carried out in a series of columnsdesigned to segregate specific products such as normally gaseoushydrocarbons, propane, butanes, light gasoline, heavy gasoline, jet fuelor kerosene, and middle distillates such as furnace oil and diesel oil.Characteristically these distillations are carried out at at leastslightly superatrnospheric pressure and in some cases at substantiallysuperatmospheric pressure. The maximum initial boiling point of theremainder is thus desirably limited to not over about 700 F. to avoidthermal degradation of the higher boiling constituents.

At least a portion of this remainder from the first, superatmospheric,distillation is further distilled to recover therefrom at least onelubricating oil base stock. The total amount of lubricating oil basestock recovered is limited in yield such that an amount thereofcorresponding to a yield of between 2% and 40% from the heavy oil feedboils within the boiling range of the heavy oil feed. That is to say,some of the lubricating oil recovered may boil below the initial boilingpoint of the fresh feed, in which case that portion is not considered incomputing whether there is recovered lubricating oil in a yield between2% and 40% by volume of the feed. The withdrawal, or not, of such aportion does, however, provide another measure of flexibility by whichproduct qualities can be maintained at desired levels in both thedistillate fuels and the lubricating oil when feed quality or otherfactors change. Similarly, if several lubricating oil products ofdifferent boiling range are recovered, the amount of each of which boilswithin the boiling range of the fresh feed must be considered indetermining the net yield. By so limiting the yield of lubricating Ollit is found that the viscosity index of a recovered lubricating oil canbe maximized, and it is further found that the viscosity index isremarkably increased as compared to the viscosity index of the feed andas compared to the amount of viscosity index increase obtainable whenthe yield is not so limited, and as compared to the amount of viscosityindex increase obtainable by previously known processes. Thus, althoughthere may be other processes which appear capable of producing oils ofmuch higher viscosity index than are obtained generally in the processof this invention, such other processes accomplish that result byemploying as the feed an oil which already has a moderately highviscosity index. By the process of this invention a much greaterincrease in viscosity index, to acceptably high levels, is obtainablewhen processing feeds of very low viscosity index as compared to theincrease in viscosity index obtained by known processes with either highor low viscosity index feeds.

The following examples serve to illustrate the practice of the inventionin certain embodiments, the importance of certain features therein, andsome of the advantages obtainable thereby as contrasted with previouslyknown processes. To simplify the description and discussion, theproperties of heavy oil feeds employed in the examples are set forthbelow:

FEED INSPECTIONS to oil boiling entirely above 700 F., there is employed3,500 barrels per day of the heavy California gas oil, which is A B C DPropane Heavy Deasphalted Heavy Gulf Heavy Arabian California Oil fromCoast Gas Oil Gas Oil Gas Oil California Resiclua Gravity, API 16. 2 l6.6 23. 9 26. 7 ,Aniline Point, F 152. 7 192. 3 183.1 172.0 Nitrogen,p.p.m 5, 650 5, 600 785 490 Sulfur, wt. percent 0.97 1. 08 0.35 2. 3Oxygen, p.p.rn 5, 500 4, 070 1,900 500 Four Point, F +120 ASTMDistillation,

percent 700 786 588 632 619 646 726 689 806 719 873 769 987 850 1, 020900 End Point 1, 077 960 Viscosity, SSU at 210 255. 9 46. 83 37. 92Viscosity Index 67 *5 *35 *87 Dewaxed The following example illustratesthe high viscosity index obtainable by the process of this inventionfrom a very low viscosity index feed.

Example 1 I taining a sulfided nickel-tungsten on silica-magnesiacatalyst. The catalyst was prepared by impregnating a silicamagnesiacracking catalyst, with nickel nitrate and ainmonium tungstate,calcining, and sulfiding. The conditions were chosen to effectapproximately 58% conversion of the combined feed and recycle todistillate fuels boiling below 700 F. The reactor eifiuent was given asimple distillation at atmospheric pressure to take off the lightgasoline fuels, and the remainder was then given a simple distillationusing stripping gas, equivalent to a vacuum distillation, to takeoverhead the heavier distillate fuels boiling up to an end point of 700F. From the stripper distillation about 13% of the highestboilingportion was withdrawn, and the rest of the highest-boiling portion notso recovered formed the aforesaid heavy recycle oil. There was thusobtained in a yield of 8.4% based on the fresh feed a lubricating oilhaving the following properties:

Gravity, API 32.1 Aniline point, F. 224.6 Pour point, F. +15 Viscosity,SSU at 100 F. 171.4 Viscosity, SSU at 210 F 44.5 Viscosity index 101.5

In a commercial installation to produce 2,000 barrels per day oflubricating oil having the above properties, there would be employed24,000 barrels per day of the heavy California gas oil feed, 13,700barrels per day of the heavy recycle oil, and there would also beobtained as products 5,000 barrels per day of a C 300- F. gasoline and20,000 barrels per day of a 300-700" F. low sulfur diesel fuel with 51octane number and below F. pour point,

In contrast to the above, when the recycle operation is not employed(based on laboratory data similarly obtained), to produce 2,000 barrelsper day of lubricating eating oil from deasphalted residuum.

Example 2 One volume of deasphalted residual oil boiling substantiallyentirely above 800 F. (Feed B), obtained in 55% yield from propanedeasphalting a California short residuum, is passed together with 0.9volume of heavy recycle oil boiling entirely above 900 F. and 5000s.c.f. hydrogen per barrel into contact with the sulfidednickeltungsten-silica-magnesia catalyst at 0.5 LHSV, 810 F., and 1800p.s.i.a. hydrogen pressure (2300 p.s.i.g. total).

From 20,000 barrels per day of deasphalted oil there is obtained bytwo-stage distillation of the products 3,000 barrels per day of C 300 F.gasoline, 3,700 barrels per day of 300-500 F. distillate, 5,300 barrelsper day of 500700 F. distillate, and 6,400 barrels per day of 700- 900F. distillate. Of the remaining 900 F.-|- material, 2,800 barrels perday is recovered, and the rest recycled. After dewaxing, the'700-900 F.distillate has a viscosity index of 68 and the 900 F.+ product has aviscosity index of 112. Products boiling within the feed boiling rangeare recovered in a yield of about 35%. (Only a portion of the 700-900 F.distillate boil-s within the feed boiling range.) In the lower boilingdistillates the ratio of middle distillate to gasoline (400700 F./C 400F.) is about 1.4. Conversion of combined fresh feed and recycle to suchlower boiling distillates, as conversion has been defined herein, isabout 32%. Thus, this example represents operation near maximum yield oflube oil and minimum conversion to lower boiling distillates within thepractice of the invention.

In contrast, however, if the deasphalted oil is passed once-through thereaction zone at the same temperature, pressure, and space velocity, 50%of the product oil still boils above 900 F. and has a viscosity indexdewaxed of only 58 and the 700-900 F. distillate has a viscosity indexof only 21.

Example 3 The deasphalted residual oil (Feed B) is passed together with1.1 volumes per volume of heavy recycle oil boiling entirely above 900F. and 5000 standard cubic feet of hydrogen per barrel into contact withthe sulfided nickel-tungsten-silica-magnesia catalyst at 0.5 LHSV, 775F., and 1800 p.s.i.a. hydrogen. From 20,000 barrels per day ofdeasphalted oil feed there is obtained by two-stage distillation of theproducts 14,500 barrels per day of distillate fuels boiling up to 700 F.A distillate lubricating oil cut boiling between 700 F. and 900 F. isrecovered in the same yield as in the preceding example, but all the 900F.+ material is recycled. Less than two-thirds of this distillatelubricating oil boils within the feed boiling range, and consequentlythe withdrawal of lubricating oil as defined herein is 21 volumepercent. The viscosity index dewaxed is 108. Included in the distillatefuels is a jet fuel boiling from 300 F. to 500 F. having the followingproperties:

Gravity, API 39.5 Aniline point, F. 130.3 ASTM smoke point, rnrn 20Freeze point, F. 85

The middle distillate to gasoline ratio is about 1.7. Thus, at the lowertemperature and smaller withdrawal of lube oil in this example, ascompared to Example 2, there is obtained a higher middle distillate togasoline ratio and a higher viscosity index product.

When the deasphalted oil is treated at the same conditions oftemperature, pressure, and space velocity without the recycle stream,8,000 barrels per day of distillate fuel-s boiling up to 700 F. areobtained per 20,000 per day of feed. 3,800 barrels per day of a 700900F. lube oil out can be distilled from the remaining material, but thelube oil so obtained has a viscosity index of only 55. The distillate inthe jet fuel boiling range has a lower smoke point and higher freezingpoint.

The following examples illustrate the production of high viscosity indexoil from straight run waxy distillates.

Example 4 The gulf coast heavy gas oil (Feed C) and 0.54 volume ofrecycle oil boiling entirely above 700 F., per volume of gas oil, arepassed with hydrogen-rich gas into contact with another Ni-W-Si-Mgcatalyst, containing slightly more nickel and less tungsten than thecatalyst in the preceding examples and prepared using a silica-magnesiapowder pressed into pellets, at 778 F., 1900 p.s.i.a. hydrogen, and 1.1LHSV. Of the normally liquid oil reaction effluent 59 volume percentboils below 700 F. Since the gas oil feed includes about 25% of materialboiling below 700 F., the conversion as defined herein is about 54%.About 28% of the combined feed and recycle boiling above 700 F. has beenconverted to 400 700 F. distillate and about 26% has been converted to C400 distillate. A portion of the reaction effluent boiling above 700 F.amounting to a yield of 11.4% based on gas oil feed is withdrawn asproduct, and the remainder forms the recycle oil. The withdrawn portionhas a viscosity index of 118 dewaxed. The distillate boiling below 700F. can be separated into 18% C 300 F. gasoline, 42% 300550 F. jet fuelwith -63 F. freeze point and 22 smoke point, and 40% 34.6 API distillatefuel with 60 cetane number, 5 F. pour point, and less than 0.01 weightpercent sulfur.

In a once-through operation at the above temperature, pressure, andspace velocity the conversion efliuent boiling above 700 F. has aviscosity index of only 89.5.

Example 5 The Arabian gas oil (Feed D) and 0.8 volume of recycle oilboiling entirely above 650 F. are contacted with a sulfidednickel-molybdenum-silica-alumina catalyst at 822 F., 1760 p.s.i.a.hydrogen, and 1.0 LHSV. This catalyst promotes the same reactions as thenickeltungsten catalysts used in previous examples, though its activityis not quite as high. Excluding overlap of distillate contained in thefeed, the conversion of oil in the combined gas oil and recycle oilboiling above 700 F. to

oil boiling below 700 F. is about 50%, 34% to C -400 gasoline and 15% to400700 F. distill-ate. When the distillates boiling up to 650 F. arewithdrawn as prod uct, and the remaining 650 F.+ material separated intolube oil product, amounting to 9% yield from gas oil feed, and recycleoil, the lube oil has a viscosity index of 119 dewaxed. This, however,is little better than can be obtained at the operating conditionswithout recycle. It will be noted that the gas oil feed employedcontains more material boiling below 700 F., and less material boilingabove 800 F., than preferred for use in practicing the invention, i.e.,as previously mentioned, at least 30% of the feed should boil above 800F. in practicing the in vention, but only about 20% of Feed D boilsabove 800 F. Also, at the conditions of this example the relativeconversion to gasoline exceeds conversion to middle distillate, whereasthe reverse situation is desired.

To recapitulate the foregoing examples, it is seen that the greatestupgrading of very low viscosity index oil to high viscosity index oiloccurs in Example 1, where the recovery of lube oil base stock islimited to below 10% yield, the feed boils substantially entirely above700 F. and about 70% above 800 F., and conversion to 400- 700 F.distillate is about 1.5 times conversion to C -400 F. distillate. Alarge improvement is obtained in Example 2 with the very heavy feed eventhough the yield of lube oil is higher, when the conversion to 400-700F. distillate is twice the conversion to C -400 F. distillate. Example 3shows that a greater viscosity index increase is obtained in a narrowboiling range by recycling a greater amount of the highest boilingremainder. In Example 4 a higher viscosity index product is obtainedwhen limited to low yield, but the upgrading of the feed is not asgreat. The high viscosity index product obtained in Example 5 reflectsthe high viscosity index of the feed, as in prior art processes.

In an embodiment similar to Example 3, a lubricating oil of maximumviscosity index can be obtained in a narrow boiling range having aninitial boiling point above the initial point of the feed, e.g. 800 F.,and an end boiling point below the end boiling oint of the feed, e.g.900 F. In a preferred embodiment of the invention maximum advantage istaken of this situation by withdrawing primarily, or only, that narrowboiling range portion as product lubricating oil, using all of thehighest boiling portion from vacuum distillation in forming the recycleoil, and using all of the lower boiling, e.g. 700800 F. cut, also informing the heavy recycle oil.

In such a situation it is found advantageous to distill under vacuumonly a portion of the remainder from atmospheric distillation of thereaction effluent so as to obtain just the desired amount of theintermediate boiling range product without the necessity of distillingthe larger amounts of material which are to be reprocessed. Thus, forexample, it is calculated that less than half of the remainder from afirst distillation to 5 50 F. end point could be subjected to vacuumdistillation, to obtain a 550- 700 F.vdistillate, a 700800 F. distillatewhich is all used in forming the heavy recycle oil, an 800900 F.distillate withdrawn as the sole lubricating oil product, and ahighest-boiling portion which is also used in forming the heavy recycleoil in combination with the 700 800 F. distillate and with the portionof 550 F.+ remainder not distilled under vacuum. In such as case therewould be a build-up of 550700 F. distillate in the recycle (becausepresent in the portion of remainder not vacuum distilled), so that theamount of recycle oil would be increased.

To avoid increasing the recycle, a preferred arrangement is to take offthe 550700 F. distillate, or a 550- 650 F. distillate, in the firstdistillation, and then to distill under vacuum only about one-third ofthe remainder to separate the 800900 F. lube oil cut from the 700- 800F. distillate and the highest boiling portion, which latter arerecycled. The ratio of heavy recycle to heavy l3 oil feed and theconversion then remain substantially un changed. It would be preferredto take off a 550650 F. distillate in the atmospheric pressuredistillation, to avoid heating the remainder too hot, in which case therecycle would increase, but only slightly.

Because of the built-in flexibility of the process, any other desiredlubricating oil out could be similarly obtained, and its viscosity indexmaximized, without adversely affecting the quality of the primary,distillate fuel, products. A particularly advantageous procedure is tothus withdraw desired narrow boiling range lube oil cuts individually,at different times, thereby facilitating their individual furthertreatment as by solvent extraction and/ or dewaxing, at the differenttreating conditions indicated as most advantageous in each case, in asingle treating plant of small size.

I claim: 1. A process for substantially entirely converting a heavy oilfeed which has (a) a viscosity index of not more than 35, (b) an endboiling point of not less than 1000" F. and (c) of which at least 30%boils above 800 F. to (i) distillates boiling below about 700 F. and(ii) improved lubricating oil base stock boiling substantially entirelyabove 700 R,

which process comprises hydrocracking said heavy oil feed in admixturewith a heavy recycle oil boiling substantially entirely .above 700 F.and containing at least a substantial portion of the highest boilingcomponents of said heavy oil feed in a catalytic hydrocracking reactionzone at conditions for converting between 20 and 40% of the combinedfeed and recycle oil which does not boil below 700 F. to distillatesboiling between 400 and 700 F. and no more than an equal amount but atleast of the combined feed and recycle oil which does not boil below 700F. to distillates boiling below 400 B,

said recycle oil being supplied in a volume ratio to heavy oil feedbetween 0.3 and 1.5,

distilling the normally liquid hydrocarbon efiluent of saidhydrocracking reaction zone to separate said efiluent into distillatesboiling below about 700 F. and a remainder boiling higher than saiddistillates,

further distilling at least a portion of said remainder to separate itat least into a distillate lubricating oil fraction and a residuallubricating oil fraction and recovering from said lubricating oilfractions at least one lubricating oil base stock in a limited yieldsuch that the portion of said total lubricating oil base stock recoveredwhich boils within the boiling range of said heavy oil feed is equal inamount to between 2% and 40% of said heavy oil feed,

and forming said heavy recycle oil by combining each portion of saidremainder boiling substantially entirely above 700 P. which was not sofurther distilled with each portion of the remainder which was sofurther distilled and boils substantially entirely above 700 F. but wasnot recovered as lubricating oil base stock, including a substantialportion of said remainder boiling over the same boiling range as a 7portion recovered as lubricating oil base stock.

2. The process of claim 1 wherein the amount of lubricating oil basestock recovered which boils within the feed boiling range is between 2%and by volume of said feed, and the volume ratio of heavy recycle oil tofeed is between 0.5 and 1.25.

3. The process of claim 1 wherein all of said remainder is distilled toobtain a gas oil distillate boiling substantially entirely above 700 F.,a distillate lubricating oil base stock, and a highestboiling portion, asubstantial amount less than all of said gas oil distillate and a minorportion of said distillate lubricating oil are withdrawn as products,and the rest of said gas oil distillate and the rest of said distillatelubricating oil are combined with 14 said highest-boiling portion toform the heavy recycle oil.

4. The process of claim 1 wherein only a portion of said remainder isdistilled to separate an amount of highest-boiling lubricating oil basestock which is withdrawn as product, from distillate boiling in the feedboiling range, and the portion of said remainder not so distilled iscombined with said distillate to form the heavy recycle oil.

5. A process for making an improved lubricating oil base stock having aviscosity index of at least about 101.5 from a low-grade heavy oil feed,which process comprises passing through a hydrocracking zone containinga nitrogen insensitive hydrocracking catalyst (1) hydrogen, (2) a heavyoil feed which as a viscosity index of not more than 35, boilssubstantially entirely above 700 F. and at least 30% above 800 F., hasan end point of not less than 1000 F. and is substantially free ofasphaltenes, and (3) a heavy recycle oil boiling substantially entirelyabove 700 F. obtained as hereinafter specified;

therein subjecting said feed and recycle to hydrocracking reactionconditions controlled in the ranges 700- 850 F., 1000-4000 p.s.i.g., andflow rate of 0.3-3 volumes of combined feed and recycle per hour pervolume of nitrogen insensitive hydrocracking catalyst so as to therebyconvert an amount between 30% and 75% of that portion of the combinedfeed and recycle which does not boil below 700 F. to distillates boilingbelow 700 F;

distilling the liquid oil eflluent of said hydrocracking zone toseparate said effiuent into distillate fuel fractions including allnormally liquid oil therein boiling in and below the kerosene boilingrange, and a higher boiling remainder boiling substantially entirelyabove 700 F.;

distilling a portion of said remainder to obtain a distillate fractionincluding hydrocarbons boiling below the initial boiling point of saidfeed, a distillate fraction suitable for use as lubricating oil basestock containing hydrocarbons boiling above the initial boiling point ofsaid feed, and another fraction suitable for use as lubricating oil basestock boiling entirely above the initial boiling point of said feed;

withdrawing an amount of said fractions limited such that the amount ofmaterial withdrawn which boils above the initial boiling point of saidfeed is between 2% and 20% by volume of said feed;

and combining the portion of said remainder not so distilled with theportions of said fractions containing material boiling above the initialboiling point of said feed which are not so withdrawn, to thereby formthe aforesaid heavy recycle oil in a volume ratio to feed between 0.3and 1.5.

6. The process of claim 5 wherein the entire liquid oil efiluent of saidhydrocracking zone is distilled at superatmospheric pressure, the entireremainder from said superatmospheric distillation is distilled undervacuum to separate distillate boiling below the initial boiling point ofsaid feed, and only a portion of the remainder from this vacuumdistillation is further distilled under vacuum to separate fractionsboiling above the initial boiling point of said feed.

7. The process of claim 6 wherein said distillate boiling below theinitial boiling point of said feed is withdrawn as a net product.

References Cited by the Examiner UNITED STATES PATENTS 3,142,634 7/1964Ireland et al. 208-94 3,142,635 7/1964 Coonradt et al 2081l1 3.174,9253/1965 Claussen et al. 2081ll DELBERT E. GANTZ, Primary Examiner.

R. RIMENS, Assistant Examiner.

1. A PROCESS FOR SUBSTANTIALLY ENTIRELY CONVERTING A HEAVY OIL FEEDWHICH HAS (A) A VISCOSITY INDEX OF NOT MORE THAN 35, (B) AN END BOILINGPOINT OF NOT LESS THAN 1000*F. AND (C) OF WHICH AT LEAST 30% BOILS ABOVE800*F. TO (I) DISILLATES BOILING BELOW ABOUT 700*F. AND (II) IMPROVEDLUBRICATING OIL BASE STOCK BOILING SUBSTANTIALLY ENTIRELY ABOVE 700*F.,WHICH PROCESS COMPRISES HYROCRACKING SAID HEAVY OIL FEED IN ADMIXTUREWITH A HEAVY RECYCLE OIL BOILING SUBSTANTIALLY ENTIRELY ABOVE 700*F. ANDCONTAINING AT LEAST A SUBSTANTIAL PORTION OF THE HIGHEST BOILINGCOMPONENTS OF SAID HEAVY OIL FEED IN A CATALYTIC HYDROCRACKING REACTIONZONE AT CONDITIONS FOR CONVERTING BETWEEN 20 AND 40% OF THE COMBINEDFEED AND RECYCLE OIL WHICH DOES NOT BOIL BELOW 700*F. TO DISTILLATESBOILING BETWEEN 400* AND 700*F. AND NO MORE THAN AN EQUAL AMOUNT BUT ATLEAST 10% OF THE COMBINED FED AND RECYCLE OIL WHICH DOES NOT BOIL BELOW700*F. TO DISTILLATES BOILING BELOW 400*F., SAID RECYLCLE OIL BEINGSUPPLIED IN A VOLUME RATIO TO HEAVY OIL FEED BETWEEN 0.3 AND 1.5,DISTILLING THE NORMALLY LIQUID HYDROCARBON EFFLUENT OF SAIDHYDROCRACKING REACTION ZONE TO SEAPRATE SAID EFFLUENT INTO DISTILLATESBOILING BELOW ABOUT 700*F. AND A REMAINDER BOILING HIGHER THAN SAIDREMAINDER FURTHER DISTILLING AT LEAST A PORTION OF SAID REMAINDER TOSEPARATE IT AT LEAST INTO A DISTILLATE LUBRICATING OIL FRACTION AND ARESIDUAL LUBRICATING OIL FRACTION AND RECOVERING FROM LUBRICATING OILFRACTIONS AT LEAST ONE LUBRICATING OIL BASE STOCK IN A LIMITED YIELDSUCH THAT THE PORTION OF SAID TOTAL LUBRICATING OIL BASE STOCK RECOVEREDWHICH BOILS WITHIN THE BOILING RANGE OF SAID HEAVY OIL FEED IS EQUAL INAMOUNT TO BETWEEN 2% AND 40% OF SAID HEAVY OIL FEED, AND FORMING SAIDHEAVY RECYCLE OIL BY COMBINING EACH PORTION OF SAID REMAINDER BOILINGSUBSTANTIALLY ENTIRELY ABOVE 700*F. WHICH WAS NOT SO FURTHER DISTILLEDWITH EACH PORTION OF THE REMAINDER WHICH WAS SO FURTHER DISTILLED ANDBOILS SUBSTANTIALLY ENTIRELY ABOVE 700*F. BUT WAS NOT RECOVERED ASLUBRICATING OIL BASE STOCK, INCLUDING A SUBSTANTIAL PORTION OF SAIDREMAINDER BOILING OVER THE SAME BOILING RANGE AS A PORTION RECOVERED ASLUBRICATING OIL BASE STOCK.